One way to save up for large purchases is to buy yourself gift cards in small increments in advance, says a reader at personal finance blog Get Rich Slowly. So if you're saving up for an iPhone, for instance, buy yourself a $20 gift card to the Apple store every few weeks. Editor J.D. Roth writes:

You can use "reverse credit" to save for more than just large items. You might use it to budget for your morning coffee, for example. If you want to limit your spending at Starbucks, put a fixed amount ($20 maybe) on a card at the beginning of the month. When that card is drained, you know you've spent your coffee budget. At the start of next month, put another $20 on the card.

As J.D. points out, this method is similar to "envelope budgeting", the classic method your grandparents used to put money aside for specific purposes.